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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

ORDINARY BRONZES

235

When cold, the mass is taken up in hot water and the brown solution
heated with sodium sulphite until it becomes pale yellow.1 The liquid is
then filtered and, the precipitate washed with water containing a little sodium
sulphide and then with hydrogen sulphide solution ; the filter is burnt in
a small dish and the residue dissolved in a little nitric acid and the solution
added to the filtrate from the metastannic acid containing the bulk of the
copper, lead, zinc, etc., dealt with as in 3.

The solution contains all the tin and antimony present as sulpho-salts.
This liquid is treated in a |-litre conical flask with 6 grams of caustic potash,
3 grams of tartaric acid and, slowly and, if necessary, with cooling, with
sufficient 30% hydrogen peroxide to give complete decoloration, that is,
to convert the sulphide completely into sulphate. The liquid is boiled
for some time to expel excess of hydrogen peroxide, allowed to cool, neu-
tralised carefully with oxalic acid, treated with an excess of 3-5 grams of
oxalic acid, diluted to 250-300 c.c., heated to boiling, and a moderate current
of hydrogen sulphide passed through the boiling liquid for about an hour.
The liquid is then allowed to cool somewhat and any precipitated antimony
sulphide collected in a tared Gooch crucible, and washed first with i%
oxalic acid solution saturated with hydrogen sulphide and afterwards with
very dilute hot acetic acid saturated with hydrogen sulphide.

To determine the tin, the filtrate is rendered slightly alkaline with
ammonia, acidified with acetic acid, and the tin precipitated with hydrogen
sulphide. After the precipitation, the liquid is left at rest for about half
an hour on the water-bath to facilitate the separation of the precipitate,
and finally filtered, being washed with hydrogen sulphide solution contain-
ing a little ammonium sulphate in solution. The tin sulphide thus obtained
is dried at 120°, converted by ignition into oxide and weighed.

2.  Determination of the Antimony.—The antimonjr sulphide in the
Gooch crucible is converted by any of the known methods 2 into the tri-
sulphide and weighed directly :   Sb2S3 X 07142 = Sb.

3.  Determination  of the  Lead,   Copper,  Iron,  Zinc,  etc.—The
filtrate obtained after the action of nitric acid on the alloy, together with
the nitric acid solution of the metals extracted from the metastannic acid,
is treated with 2-3 c.c. of cone, sulphuric acid, the further procedure being
as given for the analysis of ordinary brasses (q.v.).

4.  Determination of the Manganese, Silver, Phosphorus, Arsenic
and Sulphur.—See preceding method.

*
* *

The compositions of bronzes vary widely with the requirements as regards
hardness, elasticity, colour, sonority, etc.

Bronzes for machine gearing and the old, highly elastic, tenacious and
resistant bronzes for cannon contained on the average 90 % Cu and 10 % Sn; those
for cocks, cast machine parts, etc., 87% Cu, 13% Sn, and often small amounts of
zinc ; those for bushes and collars, 82-84% Cu and 16-18% Sn. Bronzes for

1  If the residue insoluble in water has a sandy aspect, the disaggegration is incom-
plete.    In such case the filter is dried and burnt and the residue again fused with
sulphur and sodium carbonate.

2  See Treadwell:   Analytical Chemistry, Vol. II.to flow immediately the elec-